1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to an LCD having a COT structure, which replaces to omit a black matrix generally formed on a TFT substrate with a stack structure color filter layers, thereby simplifying a fabrication process, improving the picture quality, and a method for manufacturing the same.
2. Description of the Related Art
The rapid progress in the semiconductor technology promoted production of LCDs having a slim profile and a lightweight characteristic, and LCD products having more excellent performance. Related art cathode ray tubes (CRTs) are widely used as information display devices having many advantages in terms of performance and price, while having many disadvantages in terms of miniaturization and portability.
Unlike the CRTs, the LCDs having advantages, such as a relatively small size, slim profile, lightweight, increased portability, and low power consumption, have attracted attentions of users, industry and researchers. The LCDs are introduced as one of the display devices actively replacing the CRTs to overcome the disadvantages of the CRT. Accordingly, more and more LCDs have been installed on most information processing apparatus requiring a display device today.
The LCD is a display device using modulation of light created in a liquid crystal cell. Generally, a voltage is applied to the liquid crystal having a specific molecular arrangement to change the specific arrangement into different molecular arrangements. Application of voltage to the liquid crystal cell converts an optical property, such as birefringence, an optical rotatory power, dichroism, and light scattering characteristics, into a visual property.
The related art LCD is manufactured by a method including forming an upper substrate and a lower substrate, followed by forming of an LC cell constituting the unit of a pixel, forming an alignment layer and rubbing the formed alignment layer, attaching the upper substrate and the lower substrate, filling liquid crystal into a space between the upper substrate and the lower substrate and sealing an liquid crystal inlet. In particular, while forming the upper substrate of the LCD, a black matrix for shielding light, and red (R), green (G) and blue (B) color filter layers are formed through a plurality of masking processes. Similarly, in forming the lower substrate of the LCD, gate lines for applying driving signals, data lines for applying data signals, and pixel electrodes for forming an electric field using applied data signals are formed through a plurality of masking processes.
However, the related art LCD has a disadvantage that the manufacturing process is complicated because the color filter layers and the pixel arrays are respectively formed on the upper substrate and the lower substrate, thereafter the lower substrate and the upper substrate are attached. In addition, the related art LCD has a drawback in low picture quality. When misalignment occurs while attaching the lower and upper substrates, the black matrix of the upper substrate does not completely shield light progressing from the lower substrate resulting in lower picture quality.
To overcome the above described disadvantages, there has been proposed a COT (Colorfilter On TFT) technique in which a pixel array including color filter layers and pixel electrodes are formed on a single glass substrate. Unlike in the related art LCD, the LCD having the COT structure includes the black matrix and the color filter layer formed on the lower substrate where TFTs and pixel electrodes are formed. Accordingly, the related art LCD having the COT structure has an advantage that the manufacturing process is simplified compared to the related art LCD having two separate substrates.
However, forming the color filter layer and the black matrix together with the TFTs require an additional masking process to form black matrix on the TFTs, which results in increased manufacturing cost in the related art LCD having the COT structure.